Aromatics processing catalysts

ABSTRACT

A method of preparing aromatics processing catalysts which comprises incorporating a noble metal with a member or members of a useful class of zeolites, with such incorporation occurring after zeolite crystallization, but prior to final catalyst particle formation, i.e. extrusion into particles. Said useful class of zeolites is characterized by a silica to alumina mole ratio of at least 12 and a Constraint Index in the approximate range of 1 to 12.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel methods of preparing an aromaticsprocessing catalyst, the catalyst itself, and the use of said catalystin the processing of aromatics, particularly in xylene isomerization.

2. Description of the Prior Art

Since the announcement of the first commercial installation ofOctafining in Japan in June, 1958, this process has been widelyinstalled for the supply of p-xylene. See "Advances in PetroleumChemistry and Refining" volume 4 page 433 (Interscience Publishers, NewYork, 1961). That demand for p-xylene has increased at remarkable rates,particularly because of the demand for terephthalic acid to be used inthe manufacture of polyesters.

Typically, p-xylene is derived from mixtures of C₈ aromatics separatedfrom such raw materials as petroleum naphthas, particularly reformates,usually by selective solvent extraction. The C₈ aromatics in suchmixtures and their properties are as follows:

    __________________________________________________________________________                              Density                                                    Freezing  Boiling  lbs./U.S.                                                  Point °F.                                                                        Point °F.                                                                       Gal.                                                __________________________________________________________________________    Ethylbenzene                                                                         -139.0                                                                            (-95° C.)                                                                    277.1                                                                            (136.2° C.)                                                                  7.26 (871.2 g/liter)                                P--xylene                                                                            55.9                                                                              ( 13.3° C.)                                                                  281.0                                                                            (138.3° C.)                                                                  7.21 (865.2 g/liter)                                M--xylene                                                                            -54.2                                                                             (-47.9° C.)                                                                  282.4                                                                            (139.1° C.)                                                                  7.23 (867.6 g/liter)                                O--xylene                                                                            -13.3                                                                             (-25.2° C.)                                                                  292.0                                                                            (144.4° C.)                                                                  7.37 (884.4 g/liter)                                __________________________________________________________________________

Principal sources are catalytically reformed naphthas and pyrolysisdistillates. The C₈ aromatic fractions from these sources vary quitewidely in composition but will usually be in the range of 10 to 32 wt. %ethylbenzene with the balance, xylenes, being divided approximately 50wt. % meta, and 25 wt. % each of para and ortho.

Individual isomer products may be separated from the naturally occurringmixtures by appropriate physical methods. Ethylbenzene may be separatedby fractional distillation although this is a costly operation. Orthoxylene may be separated by fractional distillation and is so producedcommercially. Paraxylene is separated from the mixed isomers byfractional crystallization.

As commercial use of para- and orthoxylene has increased there has beeninterest in isomerizing the other C₈ aromatics toward an equilibrium mixand thus increasing yields of the desired xylenes. At present, severalxylene isomerization processes are available and in commercial use.

The isomerization process operates in conjunction with the productxylene separation processes. A virgin C₈ aromatics mixture is fed tosuch a processing combination in which the residual isomers emergingfrom the product separation steps are then charged to the isomerizerunit and the effluent isomerizate C₈ aromatics are recycled to theproduct separation steps. The composition of isomerizer feed is then afunction of the virgin C₈ aromatic feed, the product separation unitperformance, and the isomerizer performance.

It will be apparent that separation techniques for recovery of one ormore xylene isomers will not have material effect on the ethylbenzeneintroduced with charge to the recovery isomerization "loop". Thatcompound, normally present in eight carbon atom aromatic fractions, willaccumulate in the loop unless excluded from the charge or converted bysome reaction in the loop to products which are separable from xylenesby means tolerable in the loop. Ethylbenzene can be separated from thexylenes of boiling point near that of ethylbenzene by extremelyexpensive "superfractionation". This capital and operating expensecannot be tolerated in the loop where the high recycle rate wouldrequire an extremely large distillation unit for the purpose. It is ausual adjunct of low pressure, low temperature isomerization as a chargepreparation facility in which ethylbenzene is separated from the virginC₈ aromatic fraction before introduction to the loop.

Other isomerization processes operate at higher pressure andtemperature, usually under hydrogen pressure in the presence ofcatalysts which convert ethylbenzene to products readily separated byrelatively simple distillation in the loop, which distillation is neededin any event to separate by-products of xylene isomerization from therecycle stream. For example, the Octafining catalyst of platinum onsilica-alumina composite exhibits the dual functions ofhydrogenation/dehydrogenation and isomerization.

The rate of ethylbenzene approach to equilibrium concentration in a C₈aromatic mixture is related to effective contact time. Hydrogen partialpressure has a very significant effect on ethylbenzene approach toequilibrium. Temperature change within the range of Octafiningconditions, i.e. 830° F. (443° C.) to 900° F. (482° C.), has but a verysmall effect on ethylbenzene approach to equilibrium.

Concurrent loss of ethylbenzene to other molecular weight productsrelates to % approach to equilibrium. Products formed from ethylbenzeneinclude C₆ +naphthenes, benzene from cracking, benzene and C₁₀ aromaticsfrom disproportionation, and total loss to other than C₈ molecularweight. C₅ and lighter hydrocarbon by-products are also formed.

The three xylenes isomerize much more selectively than doesethylbenzene, but they do exhibit different rates of isomerization andhence, with different feed composition situations the rates of approachto equilibrium vary considerably.

Loss of xylenes to other molecular weight products varies with contacttime. By-products include naphthenes, toluene, C₉ aromatics and C₅ andlighter hydrocracking products.

Ethylbenzene has been found responsible for a relatively rapid declinein catalyst activity and this effect is proportional to itsconcentration in a C₈ aromatic feed mixture. It has been possible torelate catalyst stability (or loss in activity) to feed composition(ethylbenzene constant and hydrogen recycle ratio) so that for any C₈aromatic feed, desired xylene products can be made with a selectedsuitably long catalyst use cycle.

The utilization of zeolites of the ZSM-5 class, (e.g. ZSM-5, ZSM-12,ZSM-35 and ZSM-38), for xylene isomerization is described in U.S. Pat.Nos. 3,856,871 and 3,856,873.

A significant improvement arose with the introduction of catalysts suchas zeolite ZSM-5 combined with a Group VIII metal such as nickel orplatinum as described in Morrison U.S. Pat. No. 3,856,872. It isdisclosed in this Morrison patent that the catalyst be preferablyincorporated in a porous matrix such as alumina. The Group VIII(hydrogenation) metal may then be added after incorporation with thezeolite in a matrix by such means as base exchange or impregnation. Inthe process of the U.S. Pat. No. 3,856,872 patent, ethylbenzene isconverted by disproportionation over this catalyst to benzene anddiethylbenzene. At temperatures in excess of 800° F. and using acatalyst comprising a zeolite of the ZSM-5 class and of reducedactivity, ethylbenzene and other single ring aromatics are converted bysplitting off side chains of two or more carbon atoms as described incopending application Ser. No. 914,645, filed June 12, 1978 now U.S.Pat. No. 4,188,282. A particularly preferred form of zeolite ZSM-5disclosed in said copending application is formed by the crystallizationof the zeolite from a solution containing metal ions, such as platinum.This procedure shall hereinafter be referred to as "co-crystallization".

The use of zeolites characterized by a silica to alumina mole ratio ofat least 12 and a Constraint Index in the approximate range of 1 to 12,i.e. the ZSM-5 class of zeolites, in conjunction with a Group VIII metalfor aromatics processing, is disclosed in U.S. Pat. Nos. 4,101,595 and4,101,597. Low pressure xylene isomerization using a zeolite catalystsuch as ZSM-5 without a metal function is described in U.S. Pat. No.4,101,596.

A further improvement in xylene isomerization, as described in U.S. Pat.No. 4,163,028, utilizes a combination of catalyst and operatingconditions which decouples ethyl benzene conversion from xylene loss ina xylene isomerization reaction, thus permitting feed of C₈ fractionswhich contain ethyl benzene without sacrifice of xylenes to conditionswhich will promote adequate conversion of ethyl benzene.

That improved process of the U.S. Pat. No. 4,163,028 patent utilizes alow acid catalyst, typified by zeolite ZSM-5 of low alumina content(SiO₂ /Al₂ O₃ mole ratio of about 500 to 3000 or greater) and which maycontain metals such as platinum or nickel. In using this less activecatalyst, the temperature is raised to 800° F. (427° C.) or higher forxylene isomerization. At these temperatures, ethylbenzene reactsprimarily via dealkylation to benzene and ethylene rather than viadisproportionation to benzene and diethylbenzene and hence is stronglydecoupled from the catalyst acid function. Since ethylbenzene conversionis less dependent on the acid function, a lower acidity catalyst can beused to perform the relatively easy xylene isomerization, and the amountof xylenes disproportionated is eliminated. The reduction of xylenelosses is important because about 75% of the xylene stream is recycledin the loop, resulting in an ultimate xylene loss of 6-10 wt. % byprevious processes. Since most of the ethylbenzene goes to benzeneinstead of benzene plus diethylbenzenes, the product value of theimproved process is better than that of prior practices.

SUMMARY OF THE INVENTION

In accordance with the present invention, there has now been discoverednovel methods of preparing an aromatics processing catalyst. Thecatalyst is prepared by incorporating a noble metal, e.g. platinum, in acationic form with a member or members of the useful zeolites of theinvention after crystallization of said zeolite, but prior to finalcatalyst particle formation. Said useful zeolites are characterized by asilica to alumina mole ratio of at least 12 and a Constraint Index inthe approximate range of 1 to 12. A typical preparaton of an aromaticsprocessing catalyst comprises the general steps of zeolitecrystallization; mulling with a suitable binder, such as alumina;extrusion to form catalyst particles; and impregnation with an activemetal. The conducting of this typical catalyst preparation in accordancewith the present invention would entail the impregnation of the zeoliteafter zeolite crystallization, but prior to extrusion (final catalystparticle formation).

Whereas the prior art discloses incorporation of an active metal, eitherduring zeolite crystallization, i.e. "co-crystallization", or afterextrusion, i.e. "post-impregnated extrudate", practicing this inventionand thus incorporating the active metal, i.e. nobel metals, aftercrystallization, but before extrusion, will result in a superioraromatics processing catalyst. The resultant catalyst of the novelmethods of the instant invention exhibits improved activity andselectivity as compared to the prior art catalysts.

Catalysts produced by the methods of the present invention areparticularly useful in xylene isomerization. The catalysts so producedare even more particularly useful in high temperature xyleneisomerization, i.e. xylene isomerizations conducted at temperatures inexcess of 800° F. (427° C.).

DESCRIPTION OF PREFERRED EMBODIMENTS

The aromatics processing catalysts produced by the novel method of thisinvention comprise a member or members of the novel class of zeolites asdefined herein, a noble metal and a binder. In practicing the method ofthe present invention, the noble metal is incorporated with the zeolitesubsequent to zeolite crystallization, but prior to extrusion (finalcatalyst particle formation). Such metal incorporation can beaccomplished either before or after the addition of a binder, e.g.,mulling with alumina, but in any event, before extrusion. The noblemetals include Ru, Rh, Pd, Ag, Os, Ir, Pt and Au.

The zeolite is to be in intimate contact with the moble metal. Suchnoble metal can be ion exchanged into the zeolite composition,impregnated therein or physically intimately admixed therewith. Suchcomponent can be impregnated in or onto the zeolite, such as, forexample, by, in the case of the preferred metal, platinum, treating thezeolite with a platinum metal-containing ion. Thus, suitable platinumcompounds include various cationic platinum compounds such as platinouschloride and various compounds containing platinum ammine or aminecomplexes. The amount of noble metal to the amount of total catalyst,i.e. zeolite and binder, can range from between about 0.005 wt. % andabout 0.5 wt. %, and preferably from between about 0.05 wt. % and about0.2 wt. %.

The crystalline zeolites utilized herein are members of a novel class ofzeolitic materials which exhibit unusual properties. Although thesezeolites have unusually low alumina contents, i.e. high silica toalumina mole ratios, they are very active even when the silica toalumina mole ratio exceeds 30. The activity is surprising, sincecatalytic activity is generally attributed to framework alumina atomsand/or cations associated with these aluminum atoms. These zeoliesretain their crystallinity for long periods in spite of the presence ofsteam at high temperature which induces irreversible collapse of theframework of other zeolites, e.g. of the X and A type. Furthermore,carbonaceous deposits, when formed, may be removed by burning at higherthan usual temperatures to restore activity. These zeolites, used ascatalysts, generally have low coke-forming activity and therfore areconducive to long times on stream between regenerations by burningcarbonaceous deposits with oxygen-containing gas such as air.

An important characteristic of the crystal structure of this novel classof zeolites is that it provides a selective constrained access to andegress from the intracrystalline free space by virtue of having aneffective pore size intermediate between the small pore Linde A and thelarge pore Linde X, i.e. the pore windows of the structure are of abouta size such as would be provided by 10-membered rings of silicon atomsinterconnected by oxygen atoms. It is to be understood, of course, thatthese rings are those formed by the regular disposition of thetetrahedra making up the anionic framework of the crystalline zeolite,the oxygen atoms themselves being bonded to the silicon (or aluminum,etc.) atoms at the centers of the tetrahedra.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminamole ratio of at least 12 are useful, it is preferred in some instancesto use zeolites having much higher silica to alumina mole ratios, i.e.1600 and above. In addition, zeolites as otherwise characterized hereinbut which are substantially free of aluminum, i.e. having silica toalumina mole ratios up to infinity, are found to be useful and evenpreferable in some instances. Such "high silica" or "highly siliceous"zeolites are intended to be included within this description. Also to beincluded in this definition are the pure silica analogs of the usefulzeolites of this invention, i.e. having absolutely no aluminum (silicato alumina mole ratio of infinity).

The novel class of zeolites, after activation, acquire anintracrystalline sorption capacity for normal hexane which is greaterthan that for water, i.e. they exhibit "hydrophobic" properties. Thishydrophobic character can be used to advantage in some applications.

The novel class of zeolites useful herein have an effective pore sizesuch as to freely sorb normal hexane. In addition, the structure mustprovide constrained access to larger molecules. It is sometimes possibleto judge from a known crystal structure whether such constrained accessexists. For example, if the only pore windows in a crystal are formed by8-membered rings of silicon and aluminum atoms, then access by moleculesof larger cross-section than normal hexane is excluded and the zeoliteis not of the desired type. Windows of 10-membered rings are preferred,although in some instances excessive puckering of the rings or poreblockage may render these zeolites ineffective.

Although 12-membered rings in theory would not offer sufficientconstraint to produce advantageous conversions, it is noted that thepuckered 12-ring structure of TMA offretite does show some constrainedaccess. Other 12-ring structures may exist which may be operative forother reasons and, therefore, it is not the present invention toentirely judge the usefulness of a particular zeolite solely fromtheoretical structural considerations.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access to molecules oflarger cross-section than normal paraffins, a simple determination ofthe "Constraint Index" as herein defined may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a sample of zeolite at atmospheric pressureaccording to the following procedure. A sample of the zeolite, in theform of pellets or extrudate, is crushed to a particle size about thatof coarse sand and mounted in a glass tube. Prior to testing, thezeolite is treated with a stream of air at 1004° F. (540° C.) for atleast 15 minutes. The zeolite is then flushed with helium and thetemperature is adjusted between 554° F. (290° C.) and 950° F. (510° C.)to give an overall conversion of between 10% and 60%. The mixture ofhydrocarbons is passed at 1 liquid hourly space velocity (i.e., 1 volumeof liquid hydrocarbon per volume of zeolite per hour) over the zeolitewith a helium dilution to give a helium to (total) hydrocarbon moleratio of 4:1. After 20 minutes on stream, a sample of the effluent istaken and analyzed, most conveniently by gas chromatography, todetermine the fraction remaining unchanged for each of the twohydrocarbons.

While the above experimental procedure will enable one to achieve thedesired overall conversion of 10 to 60% for most zeolite samples andrepresents preferred conditions, it may occassionally be necessary touse somewhat more severe conditions for samples of very low activity,such as those having an exceptionally high silica to alumina mole ratio.In those instances, a temperature of up to about 1004° F. (540° C.) anda liquid hourly space velocity of less than one, such as 0.1 or less,can be employed in order to achieve a minimum total conversion of about10%.

There also may be instances where the activity is so low, e.g. silica toalumina mole ratio approaching infinity, that the Constraint Indexcannot be adequately measured, if at all. In such situations, ConstraintIndex is meant to mean the Constraint Index of the exact same substance,i.e. same crystal structure as determined by such means as X-raydiffraction pattern, but in a measurable form, e.g. high aluminumcontaining form.

The "Constraint Index" is calculated as follows: ##EQU1##

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a Constraint Index of 1 to 12. ConstraintIndex (C.I.) values for some typical materials are:

    ______________________________________                                                         C.I.                                                         ______________________________________                                        ZSM-4              0.5                                                        ZSM-5              8.3                                                        ZSM-11             8.7                                                        ZSM-12             2                                                          ZSM-23             9.1                                                        ZSM-35             4.5                                                        ZSM-38             2                                                          ZSM-48             3.4                                                        TMA Offretite      3.7                                                        Clinoptilolite     3.4                                                        Beta               0.6                                                        H-Zeolon (Mordenite)                                                                             0.4                                                        REY                0.4                                                        Amporphous Silica- 0.6                                                        Alumina                                                                       Erionite           38                                                         ______________________________________                                    

The above-described Constraint Index is an important and even criticaldefinition of those zeolites which are useful in the instant invention.The very nature of this parameter and the recited technique by which itis determined however, admit of the possiblity that a given zeolite canbe tested under somewhat different conditions and thereby exhibitdifferent Constraint indices. Constraint Index seems to vary somewhatwith severity of operation (conversion) and the presence or absence ofbinders. Likewise, other variables such as crystal size of the zeolite,the presence of occluded contaminants, etc., may affect the ConstraintIndex. Therefore, it will be appreciated that it may be possible to soselect test conditions as to establish more than one value in the rangeof 1 to 12 for the Constraint Index of a particular zeolite. Such azeolite exhibits the constrained access as herein defined and is to beregarded as having a Constraint Index in the range of 1 to 12. Alsocontemplated herein as having a Constraint Index in the range of 1 to 12and therefore within the scope of the defined novel class of highlysiliceous zeolites are those zeolites which, when tested under two ormore sets of conditions within the above-specified ranges of temperatureand conversion, produce a value of the Constraint Index slightly lessthan 1, e.g. 0.9, or somewhat greater than 12, e.g. 14 or 15, with atleast one other value within the range of 1 to 12. Thus, it should beunderstood that the Constraint Index value as used herein is aninclusive rather than an exclusive value. That is, a crystalline zeolitewhen identified by any combination of conditions within the testingdefinition set forth herein as having a Constraint Index in the range of1 to 12 is intended to be included in the instant novel zeolitedefinition whether or not the same identical zeolite, when tested underother of the defined conditions, may give a Constraint Index valueoutside of the range of 1 to 12.

The novel class of zeolites defined herein is exemplified by ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similarmaterials.

XSM-5 is described in greater detail in U.S. Pat. Nos. 3,702,886 and Re.29,948. The entire descriptions contained within those patents,particularly the X-ray diffraction pattern of therein disclosed ZSM-5,are incorporated herein by reference.

ZSM-11 is described in U.S. Pat. No. 3,709,979. That description, and inparticular the X-ray diffraction pattern of said ZSM-11, is incorporatedherein by reference.

ZSM-12 is described in U.S. Pat. No. 3,832,449. That description, and inparticular the X-ray diffraction pattern disclosed therein, isincorporated herein by reference.

ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire contentsthereof, particularly the specification of the X-ray diffraction patternof the disclosed zeolite, is incorporated herein by reference.

ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of thatzeolite, and particularly the X-ray diffraction pattern thereof, isincorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. Thedescription of that zeolite, and particularly the specified X-raydiffraction pattern thereof, is incorporated herein by reference.

ZSM-48 is described in U.S. application Ser. No. 13,640, filed Feb. 21,1979.

The composition ZSM-48 can be identified, in terms of moles of anhydrousoxides per 100 moles of silica, as follows:

    (0 to 15)RN:(0 to 1.5)M.sub.2 /.sub.n O:(0 to 2)Al.sub.2 O.sub.3 :(100)SiO.sub.2

wherein M is at least one cation having a valence n, RN is a C₁ -C₂₀organic compound having at least one amine functional group of pK_(a)≦7, and wherein the composition is characterized by the distinctiveX-ray diffraction pattern as shown in Table 1 below.

It is recognized that, particularly when the composition containstetrahedral, framework aluminum, a fraction of the amine functionalgroups may be protonated. The doubly protonated form, in conventionalnotation, would be (RNH)₂ O and is equivalent in stoichiometry to 2RN+H₂O.

The X-ray diffraction pattern of the ZSM-48 has the followingsignificant lines:

                  TABLE 1                                                         ______________________________________                                        CHARACTERISTIC LINES OF ZSM-48                                                d          Relative Intensity                                                 ______________________________________                                        11.9       W-S                                                                10.2       W                                                                  7.2        W                                                                  5.9        W                                                                  4.2        VS                                                                 3.9        VS                                                                 3.6        W                                                                  2.85       W                                                                  ______________________________________                                    

These values were determined by standard techniques. The radiation wasthe K-alpha doublet of copper, and a scintillation counter spectrometerwith a strip chart pen recorder was used. The peak heights I, and thepositions as a function of 2 times theta, where theta is the Braggangle, were read from the spectrometer chart. From these, the relativeintensities, 100 I/I_(o), where I_(o) is the intensity of the strongestline or peak, and d (obs.), the interplanar spacing in A, correspondingto the recorded lines, were calculated. In Table 1 the relaiveintensities are given in terms of the symbols W=weak, VS=very strong andW-S=weak-to-strong.Ion exchange of the sodium ion with cations revealssubstantially the same pattern with some minor shifts in interplanarspacing and variation in relative intensity. Other minor variations canoccur depending on the silicon to aluminum mole ratio of the particularsample, as well as if it has been subjected to thermal treatment.

ZSM-48 can be prepared from a reaction mixture containing a source ofsilica, RN, an alkali metal oxide, e.g. sodium, water, and optionallyalumina, and having a composition, in terms of mole ratios of oxides,falling within the following ranges:

    ______________________________________                                        REACTANTS       BROAD      PREFERRED                                          ______________________________________                                        Al.sub.2 O.sub.3 /SiO.sub.2                                                                 =     0      to 0.02                                                                             0      to 0.01                               Na/SiO.sub.2  =     0      to 2  0.1    to 1.0                                RN/SiO.sub.2  =     0.01   to 2.0                                                                              0.05   to 1.0                                OH.sup.- /SiO.sub.2                                                                         =     0      to 0.25                                                                             0      to 0.1                                H.sub.2 O/SiO.sub.2                                                                         =     10     to 100                                                                              20     to 70                                 H + (added)/SiO.sub.2                                                                       =     0      to 0.2                                                                              0      to 0.05                               ______________________________________                                    

wherein RN is a C₁ -C₂₀ organic compound having amine functional groupof pK_(a) ≦7, and maintaining the mixture at 80°-250° C. until crystalsof ZSM-48 are formed. H+(added) is moles acid added in excess of themoles of hydroxide added. In calculating H+(added) and OH values, theterm acid (H+) includes both hydronium ion, whether free or coordinated,and aluminum. Thus aluminum sulfate, for example, would be considered amixture of aluminum oxide, sulfuric acid, and water. An aminehydrochloride would be a mixture of amine and HCl. In preparing thehighly siliceous form of ZSM-48, no alumina is added. The only aluminumpresent occurs as an impurity.

Preferably, crystallization is carried out under pressure in anautoclave or static bomb reactor, at 176° F. (80° C.) to 482° F. (250°C.). Thereafter, the crystals are separated from the liquid andrecovered. The composition can be prepared utilizing materials whichsupply the appropriate oxide. Such compositions include sodium silicate,silica hydrosol, silica gel, silicic acid, RN, sodium hydroxide, sodiumchloride, aluminum sulfate, sodium aluminate, aluminum oxide, oraluminum itself. RN is a C₁ -C₂₀ organic compound containing at leastone amine functional group of pK_(a) ≦7 and includes such compounds asC₃ -C₁₈ primary, secondary, and tertiary amines, cyclic amine, such aspiperidine, pyrrolidine and piperazine, and polyamines such as NH₂--C_(n) H_(2n) --NH₂ wherein n is 4-12.

It is to be understood that by incorporating by reference the foregoingpatents to describe examples of specific members of the novel class withgreater particularly, it is intended that identification of the thereindisclosed crystalline zeolites be resolved on the basis of theirrespective X-ray diffraction patterns. As discussed above, the presentinvention contemplates utilization of such catalysts wherein the moleratio of silica to alumina is essentially unbounded. The incorporationof the identified patents should therefore not be construed as limitingthe disclosed crystalline zeolites to those having the specificsilica-alumina mole ratios discussed therein, it now being known thatsuch zeolites may be substantially aluminum-free and yet, having thesame crystal structure as the disclosed materials, may be useful or evenpreferred in some applications. It is the crystal structure, asidentified by the X-ray diffraction "fingerprint", which establishes theidentity of the specific crystalline zeolite material.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intracrystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 1004° F. (540° C.) for one hour, for example, followed bybase exchange with ammonium salts followed by calcination at 1004° F.(540° C.) in air. The presence of organic cations in the formingsolution may not be absolutely essential to the formation of this typezeolite; however, the presence of these cations does appear to favor theformation of this special class of zeolite. More generally, it isdesirable to activate this type catalyst by base exchange with ammoniumsalts followed by calcination in air at about 1004° F. (540° C.) forfrom about 15 minutes to about 24 hours.

Natural zeolites may sometimes be converted to zeolite structures of theclass herein identified by various activation procedures and othertreatments such as base exchange, steaming, alumina extraction andcalcination, alone or in combinations. Natural minerals which may be sotreated include ferrierite, brewsterite, stilbite, dachiardite,epistilbite, heulandite, and clinoptilolite.

The preferred crystalline zeolites for utilization herein include ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48, with ZSM-5 beingparticularly preferred.

In a preferred aspect of this invention, the zeolites hereof areselected as those providing among other things a crystal frameworkdensity, in the dry hydrogen form, of not less than about 100 lbs. percubic foot (1.6 grams per cubic centimeter). It has been found thatzeolites which satisfy all three of the discussed criteria are mostdesired for several reasons. When hydrocarbon products or by-productsare catalytically formed, for example, such zeolites tend to maximizethe production of gasoline boiling range hydrocarbon products.Therefore, the preferred zeolites useful with respect to this inventionare those having a Constraint Index as defined above of about 1 to about12, a silica to alumina mole ratio of at least about 12 and a driedcrystal density of not less than about 1.6 grams per cubic centimeter.The dry density for known structures may be calculated from the numberof silicon plus aluminum atoms per 1000 cubic Angstroms, as given, e.g.,on page 19 of the article ZEOLITE STRUCTURE by W. M. Meier. This paper,the entire contents of which are incorporated herein by reference, isincluded in PROCEEDINGS OF THE CONFERENCE ON MOLECULAR SIEVES (London,April 1967) published by the Society of Chemical Industry, London, 1968.

When the crystal structure is unknown, the crystal framework density maybe determined by classical pycnometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. Or, the crystaldensity may be determined by mercury porosimetry, since mercury willfill the interstices between crystals but will not penetrate theintracrystalline free space.

It is possible that the unusual sustained activity and stability of thisspecial class of zeolites is associated with its high crystal anionicframework density of not less than about 1.6 grams per cubic centimeter.This high density must necessarily be associated with a relatively smallamount of free space within the crystal, which might be expected toresult in more stable structures. This free space, however, is importantas the locus of catalytic activity.

Crystal framework densities of some typical zeolites, including somewhich are not within the purview of this invention, are:

    ______________________________________                                                 Void      Framework                                                           Volume    Density                                                             cc/cc     g/cc      lb/ft.sup.3                                      ______________________________________                                        Ferrierite 0.28        1.76      109.9                                        Mordenite  .28         1.7       106.1                                        ZSM-5, -11 .29         1.79      111.7                                        ZSM-12     --          1.8       112.4                                        ZSM-23     --          2.0       124.9                                        Dachiardite                                                                              .32         1.72      107.4                                        L          .32         1.61      100.5                                        Clinoptilolite                                                                           .34         1.71      106.8                                        Laumontite .34         1.77      110.5                                        ZSM-4      .38         1.65      103.0                                        (Omega)                                                                       Heulandite .39         1.69      105.5                                        P          .41         1.57      98.0                                         Offretite  .40         1.55      96.8                                         Levynite   .40         1.54      96.2                                         Erionite   .35         1.51      94.3                                         Gmelinite  .44         1.46      91.2                                         Chabazite  .47         1.45      90.5                                         A          .5          1.3       81.1                                         Y          .48         1.27      79.2                                         ______________________________________                                    

When synthesized in the alkali metal form, the zeolite can beconveniently converted to the hydrogen form, generally by intermediateformation of the ammonium form as a result of ammonium ion exchange andcalcination of the ammonium form to yield the hydrogen form. In additionto the hydrogen form, other forms of the zeolite wherein the originalalkali metal has been reduced to less than about 1.5 percent by weightmay be used.

As is the case of many catalysts, it is desired to incorporate thezeolite with another material resistant to the temperatures and otherconditions employed in organic conversion processes. Such materialsinclude active and inactive materials as well as inorganic material suchas clays, silica and/or metal oxides. Inactive materials suitably serveas diluents to control the amount of conversion in a given process tothat products can be obtained economically and orderly without employingother means for controlling the ratio of reaction.

Binders useful for compositing with the useful zeolite herein alsoinclude inroganic oxides, notably alumina, which is particularlypreferred.

In addition to the foregoing materials, the zeolite catalyst can becomposited with a porous matrix material such as silica-alumina,silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia. The relative proportions of finely dividedcrystalline zeolite and inorganic oxide matrix vary widely with thezeolite content ranging from about 1 to about 90 percent by weight andmore usually in the range of about 2 to about 50 percent by weight ofthe composite.

It may be preferred to use a catalyst of controlled acid activity inmany processes and process conditions embraced by the present invention.This controlled acid activity of the catalyst is attainable in any ofseveral ways or a combination of these. A preferred method to reduceactivity is to form the zeolite at high silica to alumina mole ratioabove 200, preferably above 500. Very high dilution with an inert matrixis also effective.For example, composites of a more active form ofzeolite ZSM-5 with alumina at a ratio of 5 parts of zeolite with 95parts of the inert matrix provide a suitable catalyst as described inU.S. Pat. No. 4,152,363, the entire contents of which are incorporatedherein by reference.

Activity of these zeolites may also be reduced by thermal treatment orsteam at high temperature as described in U.S. Pat. Nos. 3,965,209 and4,016,218, the entire contents of which are incorporated by referenceherein. Zeolites employed in such severe reactions as aromatization ofparaffins and olefins lose activity to an extent which makes themsuitable for use in the process of this invention. See U.S. Pat. No.3,960,978 for fuller discussion of this manner of deactivated zeolite,the entire contents of which are incorporated by reference herein.Another method for reducing activity is to provide basic cations such assodium at a significant proportion of the cationic sites of the zeolite.That technique is described in U.S. Pat. No. 3,899,544, the entirecontents of which are incorporated by reference herein.

By whatever means the controlled acid activity is achieved, the activitymay be measured in terms of disproportionation activity. A suitable testfor this purpose involves contacting xylenes in any convenient mixtureor as a single pure isomer over the catalyst at 900° F. (482° C.), 200psig (1480 kPa) and liquid hourly space velocity (LHSV) of 5. Suitablecatalysts for use in the process of this invention will show a singlepass loss of xylenes (by disproportionation) of less than 2 weightpercent, preferably less than one percent. Catalysts which have beenemployed show losses in the neighborhood of 0.5 percent. Itis this verylow rate of disproportionation at very high levels of ethyl benzeneconversion to benzene (about 30%) that provides the advantage of the newchemistry of aromatics processing characteristic of this invention. Thatlack of disproportionation (and transalkylation generally) activity alsodictates withdrawal of compounds boiling above and below eight carbonatom aromatic compounds. For example, toluene and trimethyl benzene areconverted to very little, if any, extent and become diluents whichoccupy reactor space to no advantage. Small amounts of such diluents canbe tolerated, such as those present by reason of "sloppy" fractionation,but withdrawal to at least a major extent is important to efficientoperation.

A preferred procedure for preparing a typical Pt-ZSM-5/Al₂ O₃ compositecatalyst according to the instant invention would comprise the followingsteps:

(1) preparing ZSM-5 by known procedures

(2) mulling the ZSM-5 with an alumina binder and water to form anextrudable mass

(3) contacting the extrudable mass of ZSM-5 and alumina binder with anaqueous platinum-containing solution such as tetraamine platinum (II)chloride

(4) extruding the Pt-ZSM-5/Al₂ O₃ to form catalyst pellets, followed bydrying

(5) calcining in nitrogen to decompose the organics in the ZSM-5

(6) base-exchanging with ammonium ion solution to remove sodium from theZSM-5

(7) drying

(8) calcining in air

(9) steam treating the final catalyst particles at about 1025° F. (552°C.).

Table 2 immediately set forth hereinbelow compares the step-wisepreparation of Pt-ZSM-5/Al₂ O₃ composite catalyst by two conventionalmethods, i.e. "post-impregnation" and "co-crystallization", and by twomethods of the instant invention, side by side, i.e. zeoliteimpregnation and composite impregnation.

                                      TABLE 2                                     __________________________________________________________________________    PREPARATION OF A Pt--ZSM-5/Al.sub.2 O.sub.3 CATALYST                          Conventional Preparation Methods                                              Post-Impregnation   Co-Crystallization                                        __________________________________________________________________________    1. Crystallization of ZSM-5                                                                       1. Crystallization of ZSM-5                                                      with Pt                                                2. Mulling with Al.sub.2 O.sub.3 binder                                                           2. Mulling with Al.sub.2 O.sub.3 binder                   3. Extrusion of ZSM-5/Al.sub.2 O.sub.3                                                            3. Extrusion of Pt--ZSM-5/Al.sub.2 O.sub.3                   into catalyst pellets                                                                             into catalyst pellets                                  4. Drying           4. Drying                                                 5. Calcining in N.sub.2                                                                           5. Calcining in N.sub.2                                   6. Base-exchange with ammonium                                                                    6. Base-exchange with ammonium                               ions                ions                                                   7. Drying           7. Drying                                                 8. Impregnation of ZSM-5/Al.sub.2 O.sub.3                                                         8. Calcining in air                                          with Pt                                                                    9. Calcining in air *9.                                                                              Steam treatment                                        *10.                                                                             Steam treatment                                                            __________________________________________________________________________    PREPARATION OF A Pt--ZSM-5/Al.sub.2 O.sub.3 CATALYST                          New Methods of this Invention                                                 Composite Impregnation                                                                            Zeolite Impregnation                                      __________________________________________________________________________    1. Crystallization of ZSM-5                                                                       1. Crystallization of ZSM-5                               2. Mulling the ZSM-5 with Al.sub.2 O.sub.3                                                        2. Impregnation of ZSM-5 with Pt                             binder                                                                     3. Impregnation of the ZSM-5/Al.sub.2 O.sub.3                                                     3. Mulling Pt--ZSM-5 with                                    with Pt             Al.sub.2 O.sub.3 binder                                4. Extrusion of Pt--ZSM-5/Al.sub.2 O.sub.3                                                        4. Extrusion of Pt ZSM-5/Al.sub.2 O.sub.3                    into catalyst pellets                                                                             into catalyst pellets                                  5. Drying           5. Drying                                                 6. Calcining in N.sub.2 and/or air                                                                6. Calcining in N.sub.2 and/or air                        7. Base-exchange with ammonium ions                                                               7. Base exchange with ammonium ions                       8. Drying           8. Drying                                                 9. Calcining in air 9. Calcining in air                                       *10.                                                                             Steam treatment  *10.                                                                             Steam treatment                                        __________________________________________________________________________     *Steam treatment is optional depending on silica/alumina mole ratio of th     zeolite (ZSM5 in these preparations).                                    

As can be seen, the preferred method of preparing Pt-ZSM-5/Al₂ O₃catalyst distinctly differs from the prior art methods of manufacturingthe catalyst. Indeed, the method of the present invention produces acatalyst with better metal distribution than the prior art methods. Alsothe catalyst produced by the method of this invention shows little or noaging in comparison with the prior art produced catalysts.

Catalysts produced by the method of this invention offer the followingadditional advantages:

The improved catalytic activity for paraffin and ethyl benzeneconversions may allow for processing unextracted feedstocks, thusreducing extensive separation/distillation costs for fractionallyseparating paraffins from xylene/ethyl benzene feeds.

The precalcination step that removes the organics (introduced duringzeolite crystallization) fixes the noble metal on the zeolite (orzeolite+Al₂ O₃), rendering it impervious to base exchange. Thus ionexchange of ammonium (hydrogen) for sodium may be done in the presenceof the affixed platinum. With the typical Ni on HZSM-5 catalyst, nickelmust be added (exchanged) at the end of the catalyst procedure. With thecatalyst produced by the method of this invention, it is feasible toback-exchange various amounts of other metals such as Ni, Cu, etc., toproduce various noble metal combinations without losing noble metal.

The catalyst manufacturing process is simplified (especially comparedwith prior co-crystallized catalysts) in that existing equipment may beused with only slight modification in procedures.

The catalyst prepared according to the novel method of the presentinvention is particularly useful in aromatics processing and mostparticularly for xylene isomerization processes such as the onedescribed in U.S. Pat. No. 4,163,028, the entire contents of which areincorporated herein by reference.

Conditions for conducting such xylene isomerizations with the catalystproduced according to the method of the present invention include atemperature of between about 500° F. (260° C.) and 1000° F. (540° C.)and preferably between aout 800° F. (430° C.) and about 900° F. (490°C.); a pressure of between about 50 psig (450 kPa) and about 1000 psig(7000 kPa), preferably from between about 100 psig (700 kPa) and about400 psig (2860 kPa); and a weight hourly space velocity of between about1 and about 50 and preferably between about 5 and about 15. It ispreferred to conduct xylene isomerization in accordance with thisinvention in the presence of hydrogen. If hydrogen is used, thehydrogen/hydrocarbon mole ratio is between about 1 and 20 preferablybetween about 3 and 8.

The specific examples, hereinafter discussed, will serve to illustratethe present invention, without unduly limiting same.

EXAMPLE 1

This example illustrates the preparation of a Pt-ZSM-5/Al₂ O₃ catalystaccording to a novel method of this invention wherein the ZSM-5 was in ahighly siliceous form and the platinum level of the finished catalystwas 0.2 wt. %. In this example, the ZSM-5 and alumina were mulled into acomposite and then impregnated with platinum, i.e. compositeimpregnation.

A sodium silicate solution was prepared by mixing 36.62 parts of sodiumsilicate (28.7 wt. % SiO₂, 8.9 wt. % Na₂ O, 21.17 parts water and 0.11parts Daxad 27 (W. R. Grace & Company).

An acid solution was prepared by adding together 3.83 parts H₂ SO₄, 4.33parts NaCl and 21.73 parts water.

The sodium silicate solution and acid solution were mixed in a stirredautoclave containing 1.05 parts water. Added to this mixed solution was2.52 parts NaCl to form a gel.

An organic solution was prepared by adding together 2.46 partstri-n-propylamine. 2.12 parts n-propylbromide and 4.07 partsmethylethylketone.

The organic solution was added to the gel and the resultant mixture washeated to 210° F. (100° C.). After crystallization was greater thanabout 50% complete, the temperature was increased to 320° F. (160° C.)for 8 hours. Unreacted organics were removed by flashing and theremaining contents were cooled. The remaining zeolite was dialyzed,dried and identified as ZSM-5 having a silica to alumina mole ratio ofabout 520.

A mixture of 49.82 parts of the above formed ZSM-5 zeolite and 49.82parts dried alumina was treated in a muller with a solution containing0.36 parts tetraamine platinum (II) chloride and with sufficient waterto extrudate the mass into 1/16 inch (0.16 cm) pellets. The extrudedmaterial contained 50 parts ZSM-5, 50 parts alumina and about 0.2 wt. %platinum.

The dried extrudate was calcined for 2.2 hours in flowing nitrogen at1000° F. (540° C.). After slowly cooling under nitrogen, the extrudatewas contacted with an ammonium nitrate exchange solution (containingabout 0.4 lbs. NH₄ NO₃ /lb. extrudate) at ambient temperature until thesodium level was reduced to below 0.1%. After said exchange, theextrudate was washed, dried and calcined in air at 1000° F. (540° C.)for 3 hours. The resultant catalyst composite was then heated in air toabout 975° F. (530° C.) and steam was gradually introduced into thereactor tube. When 100% steam was attained, the temperature was adjustedto 1025° F. (550° C.) and held constant for 3 hours. The catalyst wasthen cooled in nitrogen.

EXAMPLE 2

The same procedure utilized in Example 1 was performed in this example,with the exception that one-half the amount of tetraamine platinum (II)chloride was used. The resultant catalyst extrudate contained 0.11 wt. %platinum.

EXAMPLE 3

The same procedure employed in Example 1 was conducted in this example,with the exception that one-fourth the amount of tetraamine platinum(II) chloride was used. The resultant catalyst extrudate contained 0.05wt. % platinum.

EXAMPLE 4

This example illustrates the preparation of a Pt-ZSM-5/Al₂ O₃ catalystaccording to a novel method of this invention wherein the ZSM-5 is in ahighly siliceous form. Whereas the catalyst prepared according toExamples 1-3 was composite impregnated, the catalyst prepared accordingto this example was zeolite impregnated.

The procedure of Example 1 was followed with the following exception:the dried zeolite was contacted with a solution of tetraamine platinum(II) chloride before addition of the alumina. After such contact, thealumina was added to the muller before extrusion and the same remainingprocedure as given in Example 1 was carried out.

EXAMPLE 5

This example illustrates the preparation of a Pt-ZSM-5/Al₂ O₃ catalystaccording to a novel method of the instant invention. In this example,the ZSM-5 had a lower silica to alumina mole ratio than that used inExamples 1-4, namely, a SiO₂ /Al₂ O₃ mole ratio of about 70. The mode ofimpregnation employed in this example was composite impregnation.

A sodium silicate solution was prepared by mixing 16 parts water and27.7 parts sodium silicate (28.7 wt. % SiO₂, 8.9 wt. % Na₂ O, 62.4%, H₂O) followed by addition of 0.08 parts Daxad 27 (W. R. Grace & Company).The solution was cooled to approximately 60° F. (15° C.).

An acid solution was prepared by adding 1 part aluminum sulfate (17.2wt. % Al₂ O₃) to 16.4 parts water followed by 2.4 parts sulfuric acid(93 wt. % H₂ SO₄) and 1.2 parts NaCl.

These solutions were mixed in an agitated vessel. A total of 5.1 partsof NaCl were added to the acid solution and gel. The gel molar ratiosexpressed as oxides are the following:

SiO₂ /Al₂ O₃ =78.4

Na₂ O/Al₂ O₃ =49.9

An organic solution was prepared by adding 1.6 parts n-propyl bromideand 3.1 parts methyl ethyl ketone to 1.9 parts tri-n-propylamine.

After the gel was heated to about 200° F. (95° C.), agitation wasreduced and the organic solution was added above the gel. This mixturewas held at about 200°-230° F. (95°-110° C.) for 14 hours, then severeagitation was resumed. When approximately 65% of the gel ascrystallized, the temperature was increased to 300°-320° F. (150°-160°C.) and held there until crystallization was complete. Unreactedorganics were removed by flashing and the remaining contents cooled.

The zeolite slurry product was diluted with 4-5 parts water per partslurry and 0.0002 parts of flocculent (Rohm & Haas Primafloc C-7) perpart slurry, allowed to settle and supernatant liquid was drawn off. Thesettled solids were reslurried to the original volume of the precedingstep with water and 0.00005 part of flocculant per part slurry. Aftersettling, the aqueous phase was decanted. This procedure was repeateduntil the sodium level of the zeolite was less than 1.0 wt. %. Thewashed zeolite was then filtered, dried and identified as ZSM-5 having asilica/alumina mole ratio of at least 12, i.e., about 70, and aconstraint index of between about 1 and 12, i.e. about 8.3.

A mixture of 49.91 parts of dried ZSM-5 zeolite and 49.91 parts driedalumina was contacted in a muller with a solution containing 0.18 partstetraamine platinum (II) chloride and with a sufficient amount of waterto form 1/16 inch (0.16 cm) pellets. The extruded material contained 50parts ZSM-5 zeolite, 50 parts alumina and 0.1 wt. % platinum.

The extrudate was dried and calcined in nitrogen for 3 hours. Thecalcined extrudate was then exchanged with ammonium nitrate solution(containing about 0.4 lbs NH₄ NO₃ /lb. extrudate) which reduced thesodium content below 0.05%. The exchanged extrudate was washed, driedand calcined in air at 1000° F. (540° C.) for 3 hours. The catalyst wasthen steamed (100% steam) at 1025° F. (550° C.) for 24-26 hours.

                                      TABLE 3                                     __________________________________________________________________________    COMPARISON OF VARIOUS AROMATICS PROCESSING CATALYSTS                          Example No.                                                                              7             8     9        10     11       12                    __________________________________________________________________________    Catalyst Type                                                                            Composite Impregnated                                                                       Ni--ZSM-5                                                                           Pure ZSM-5 cc Pt                                                                       ZSM-5 cc Pt                                                                          Post-Impregnated                                                                       Bulk Diluted                     Pt--ZSM-5/alumina (high      Extrudate                                        silica/alumina mole ratio)                                         Temperature, °F.                                                                  871           626   899      873    899      902                   EB Conversion, %                                                                         65.2          36.0  35.0     52.0   56.6     50.5                  Xylene Loss, %                                                                           1.4           5.2   0.2      1.0    1.0      0.6                   Ring Loss, %                                                                             0.9           -0.2  0.3      0.5    0.3      0.6                   n-C.sub.9 Comversion, %                                                                  91.7          98.0  61.9     63.5   70.5     78.2                  i-C.sub.8 Conversion, %                                                                  28.0          13.6  12.8     25.9   13.9     29.7                  C.sub.6 H.sub.6 /ΔEB (moles)                                                       0.77          0.40  0.81     0.83   0.79     0.82                  C.sub.2 /ΔEB                                                                       0.89          0     0.92     0.96   0.85     0.90                  C.sub.2.sup.= /C.sub.2                                                                   0.08          0     0.12     0.09   0.1      0.09                  p-Xyl/(p-Xyl)eq. %                                                                       105           105   101      105    105      106                   Pt, ppm    2000          9400(Ni)                                                                            7600     1400   2000     75                               (0.2% Pt on                                                                   total catalyst)                                                    __________________________________________________________________________

EXAMPLE 6

In this example, the same procedure as used in Example 5 was conducted,with the following exception: the dried zeolite was contacted with theplatinum containing solution before addition of the alumina. The aluminawas added to the muller and the contents were extruded forming 1/16 inch(0.16 cm) pellets. The remaining procedure of Example 5 was followedresulting in a zeolite impregnated catalyst containing 0.1% Pt. and0.03% sodium.

EXAMPLES 7-12

The composite impregnated high silica/alumina ZSM-5 with 0.2 wt. % Ptcatalyst prepared according to Example 1 was compared against variousconventional catalysts in Examples 7-12. The results for this comparisonare given in Table 3. All the catalysts used in Examples 7-12 were incontact with the following chargestock:

    ______________________________________                                               Ethylbenzene                                                                           14%                                                                  p-Xylene 9%                                                                   m-Xylene 65%                                                                  o-Xylene 6%                                                                   i-C.sub.8 H.sub.18                                                                     3%                                                                   n-C.sub.9 H.sub.20                                                                     3%                                                            ______________________________________                                    

The catalysts used in Examples 7-12 were contacted with the aforesaidchargestock at the following reaction conditions:

    ______________________________________                                        WHSV            6.8                                                           H.sub.2 /HC     6.5-7                                                         Pressure        200 psig (1480 kPa)                                           Temperature     600-900° F. (316-482° C.)                       ______________________________________                                    

The catalyst utilized in Example 7 represents a catalyst preparedaccording to one of the improved methods of this invention and preparedaccording to the general procedure of Example 1.

The catalyst employed in Example 8 was a conventional commercialaromatics processing catalyst, namely Ni-ZSM-5/Al₂ O₃ containing 0.94%Ni. The catalyst of Example 9 was pure ZSM-5 co-crystallized withplatinum (ZSM-5 cc Pt) containing 0.76% Pt and with the ZSM-5 having asilica to alumina mole ratio of 1040. A bound extrudate version of thecatalyst of Example 9 was used in Example 10. This catalyst had azeolite to alumina binder ratio of 35/65 and a platinum content of0.14%. In Example 11, a post-impregnated extrudate catalyst wasemployed. This catalyst contained ZSM-5 with a 70/1 silica to aluminamole ratio and was steamed for 16 hours at 1050° F. to control zeoliteactivity. In Example 12, a bulk diluted HZSM-5 extrudate impregnated tocontain 75 ppm Pt and 1 wt. % ZSM-5 (99% alumina) was utilized.

The superior catalytic properties (activity and selectivity) of thecatalyst prepared according to one of the methods of this invention areclearly demonstrated in comparison with other catalysts in Table 3. Thehighest ethylbenzene (EB) conversion (65.2%) was attained with thecatalyst produced by the instant invention. This catalyst alsodemonstrated very good selectivity with a xylene loss of less than 1.5%.The catalyst prepared according to one of the novel methods of thisinvention also showed very good activity for paraffin conversion. Incomparison with all the other platinum-containing catalysts of Table 3,the catalyst prepared according to Example 1 gave the best conversion ofn-C₉. The fact that this catalyst demonstrates high activity forparaffin conversion would be significant in processing unextractedfeedstocks, e.g. C₈ reformate cuts which contain paraffins andnaphthenes.

EXAMPLE 13

The composite impregnated, high silica/alumina ZSM-5 with 0.11 wt. % Ptcatalyst prepared according to Example 2 was contacted with anethylbenzenexylene-paraffin feed at the following conditions:

    ______________________________________                                        WHSV              7 and 13.7                                                  H.sub.2 /HC       about 7                                                     Pressure          200 psig (1480 kPa)                                         Temperature       877° F. (470° C.)                             ______________________________________                                    

The feedstock composition was as follows:

    ______________________________________                                               Ethylbenzene                                                                           14%                                                                  p-Xylene 12%                                                                  m-Xylene 62%                                                                  o-Xylene  6%                                                                  i-C.sub.8 H.sub.18                                                                      3%                                                                  n-C.sub.9 H.sub.20                                                                      3%                                                           ______________________________________                                    

The results of this example are given below in Table 4.

                  TABLE 4                                                         ______________________________________                                        Temperature, °F.                                                                        877      877                                                 WHSV             7.0      13.7                                                EB Conversion, % 64.8     41.6                                                Xylene Loss, %   1.3      0.55                                                Ring Loss, %     0.9      0.3                                                 n-C.sub.9 Conversion, %                                                                        79.15    49.1                                                i-C.sub.8 Conversion, %                                                                        27.8     18.4                                                C.sub.6 H.sub.6 /ΔEB (Moles)                                                             0.74     0.79                                                C.sub.2 /ΔEB                                                                             0.88     0.87                                                C.sub.2.sup.= /C.sub.2                                                                         0.07     0.13                                                p-Xyl/(p-Xyl)eq. %                                                                             105      105                                                 ppm Pt           1000     1000                                                ______________________________________                                    

EXAMPLES 14-15

These examples illustrate the effects of steaming low silica/aluminamole ratio zeolite catalyst prepared according to this invention. Thefeedstock utilized in these examples was the same as that givenpreviously in Example 13. The catalysts employed in these examples wereprepared according to Example 5. The results for these examples aregiven in Table 5.

                  TABLE 5                                                         ______________________________________                                                     Example 14   Example 15                                          ______________________________________                                        Catalyst Preparation                                                                         Steamed at 1025° C.                                                                   Not steamed                                                    for 36 hours                                                   Reaction Conditions                                                           Temperature, °F.                                                                      871            870                                             WHSV           6.8            6.9                                             Pressure, psig 200            200                                             H.sub.2 /HC    5.6            5.6                                             Conversions and Losses:                                                       EB Conv., %    63.5           98.3                                            n-C.sub.9 Conv., %                                                                           59.7           99.5                                            i-C.sub.8 Conv., %                                                                           17.0           53.1                                            Xylene Loss, % 1.6            26.1                                            Ring Loss, %   0.3            3.7                                             p-Xyl/(p-Xyl)eq. %                                                                           104.9          105.2                                           ______________________________________                                    

It is evident from the above that steaming is preferred for a lowsilica/alumina mole ratio zeolite containing catalyst to drasticallyreduce both xylene and ring losses.

EXAMPLES 16-17

These examples illustrate the effects of steaming on high silica/aluminamole ratio zeolite catalysts prepared according to this invention. Thefeedstock utilized for these examples was the same as that givenpreviously in Example 13. The catalysts employed in these examples wereprepared according to the general procedure of Example 1, with theexception that steaming step was in accordance with that given below inTable 6. The results for these examples are given in Table 6.

                  TABLE 6                                                         ______________________________________                                                     Example 16   Example 17                                          ______________________________________                                        Catalyst Preparations                                                                        Steamed at 1025° F.                                                                   Unsteamed                                                      for 3 Hours                                                    Reaction Conditions:                                                          Temperature, °F.                                                                      871° F. 870° F.                                  WHSV           6.9            6.7                                             Pressure, psig 200            200                                             H.sub.2 HC (approx.)                                                                         7              7                                               Conversions and Losses:                                                       EB Conversion, %                                                                             66.0           54.9                                            Xylene Loss, % 1.8            2.1                                             Ring Loss, %   1.3            1.9                                             n-C.sub.9 Conversion, %                                                                      93.2           99.5                                            i-C.sub.8 Conversion, %                                                                      30.3           47.4                                            C.sub.6 H.sub.6 /ΔEB (Moles)                                                           0.76           0.73                                            C.sub.2 /ΔEB                                                                           0.87           0.81                                            C.sub.2.sup.= /C.sub.2                                                                       0.08           0.05                                            p-Xyl/(p-Xyl)eq. %                                                                           104.7          104.7                                           ______________________________________                                    

From studying the above, it is noticed that for high silica/alumina moleratio zeolite catalysts, steaming increases the activity for EBconversion, while slightly decreasing xylene and ring losses and alsoreducing activity for paraffin conversion.

What is claimed is:
 1. A method for preparing a noble metal-containingzeolite catalyst which comprises incorporating a noble metal in acationic form with a zeolite after crystallization of the zeolite, priorto final catalyst particle formation and prior to any calcination orsteaming of said zeolite, said zeolite being characterized by a silicato alumina mole ratio of at least 12 and a Constraint Index in theapproximate range of 1 to
 12. 2. The method of claim 1 wherein saidnoble metal is one or more members selected from the group consisting ofruthenium, rhodium, palladium, silver, osmium, iridium, platinum andgold.
 3. The method of claim 2 wherein said noble metal is platinum. 4.The method of claim 1 wherein said zeolite is one or more membersselected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-23,ZSM-35, ZSM-38 and ZSM-48.
 5. The method of claim 4 wherein said zeoliteis ZSM-5.
 6. The method of claim 1 wherein incorporating said noblemetal with said zeolite occurs via ion exchange.
 7. The method of claim1 wherein incorporating said noble metal with said zeolite occurs viaimpregnation.
 8. The method of claim 1 wherein incorporating said noblemetal with said zeolite occurs via physical initimate admixing.
 9. Themethod of claim 1 wherein the noble metal content ranges from betweenabout 0.005 wt. % and about 0.5 wt. % of total catalyst.
 10. The methodof claim 9 wherein the noble metal content ranges from between about0.05 wt. % and about 0.20 wt. % of total catalyst.
 11. The method ofclaim 1 wherein said zeolite is mulled with a binder before saidincorporation with the noble metal, but prior to final catalyst particleformation.
 12. The method of claim 1 wherein a binder is added afterincorporating the noble metal with the zeolite, but prior to finalcatalyst particle formation.
 13. The method of claim 11 wherein saidbinder is alumina.
 14. The method of claim 12 wherein said binder isalumina.
 15. The method of claim 1 wherein said catalyst is ofcontrolled acid activity.
 16. The method of claim 15 wherein saidcontrolled acid activity is achieved by utilizing a zeolite with a highsilica to alumina mole ratio.
 17. The method of claim 16 wherein saidhigh silica to alumina mole ratio is above
 200. 18. The method of claim17 wherein said high silica to alumina mole ratio is above
 500. 19. Themethod of claim 15 wherein said controlled acid activity is achieved bysteam treatment of the catalyst.
 20. The method of claim 15 wherein saidcontrolled acid activity is achieved by utilizing a zeolite having asignificant proportion of its cationic sites occupied by basic cations.21. The method of claim 20 wherein said basic cations are sodiumcations.
 22. The method of claim 15 wherein said controlled acidactivity is achieved by utilizing a zeolite with a high silica toalumina mole ratio in combination with steam treatment of the catalyst.23. The method of claim 22 wherein said high silica to alumina moleratio is above
 200. 24. The method of claim 23 wherein said high silicato alumina mole ratio is above
 500. 25. The catalyst produced by themethod of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, 20, 21, 22, 23 or
 24. .Iadd.
 26. An improved method forpreparing a composite zeolite-alumina catalyst wherein a crystallinezeolite having a silica to alumina mole ratio of at least 200 and aConstraint Index of about 1 to 12 has controlled acid activity byutilizing said zeolite in combination with alumina binder and steamtreatment at elevated temperature;which comprises incorporating a noblemetal in a cationic form with the zeolite after crystallization of thezeolite, prior to final composite catalyst formation and prior to anycalcination or steaming of the zeolite..Iaddend. .Iadd.27. In the methodfor preparing a composite zeolite-alumina catalyst according to claim26, the further improvement wherein said noble metal consistsessentially of platinum and wherein said zeolite consists essentially ofacid ZSM-5 and wherein said zeolite noble metal and alumina areintimately mixed by mulling prior to final composite catalyst particleformation..Iaddend. .Iadd.28. In the method for preparing a compositezeolite-alumina catalyst according to claim 27, the further improvementwherein said zeolite mole ratio is about 500 and platinum content rangesbetween about 0.005 wt. % and about 0.05 wt. % of totalcatalyst..Iaddend. .Iadd.29. In the method for preparing a compositezeolite-alumina catalyst wherein a crystalline zeolite having a silicato alumina mole ratio of at least 200 and a Constraint Index of about 1to 12 has controlled acid activity by utilizing said zeolite incombination with alumina binder and steam treatment at elevatedtemperature; the improvement which comprises mulling alumina binder withthe zeolite and water to form an extrudable mass; forming the compositecatalyst by extrusion of the zeolite-alumina mixture, calcining theextrudate composite, and steam treating the calcined composite..Iaddend..Iadd.30. In the method for preparing a composite zeolite-aluminacatalyst according to claim 29, the further improvement wherein acidZSM-5 zeolite is incorporated with about 0.005 wt. % to 0.5 wt. %platinum prior to final composite catalyst formation and prior to anycalcination of the zeolite..Iaddend. .Iadd.31. A catalyst produced bythe method of claim 26, 27, 28, 29 or 30..Iaddend.